Le Lion Devenu Vieux (1932, 3.5MB, 1:04 sec.)

Ladislas Starewitch is often credited with inventing stop motion animation
as we know it, though so are several other people. It depends on what fits
into your definition of stop motion.
Certainly he was probably the first to actually make little figures and move
them frame by frame in an attempt to duplicate lifelike movement of actual
living things. it was because he was filming beetles and found that the hot
lights made them lethargic, so he made his own little beetles asrealistically
as possible and animated them instead.
This gave birth to further projects with very lifelike but sometimes partially
anthropomorphic (human-like) animals.
from – Darkstrider.

By Mica. (thanks Adam)